1. Field of the Invention
This invention is directed to sample holders utilized in vertical beam photometers and to techniques for improving the reliability of assays conducted using such sample holders.
2. Description of the Background
Microplates, which are molded plastic plates having a number of small depressions known as wells in which individual reactions can be carried out, are useful in a wide variety of chemical and biochemical applications in which a number of related procedures are carried out at the same time. Originally, photometry on the contents of such microplates was accomplished by withdrawing samples from the wells and conducting an assay in a different location (e.g., in the cuvette of a spectrophotometer) to determine the content of each individual well. More recently, the technique of vertical beam photometry has been utilized to conduct a direct assay in the individual wells. The microplate is placed in a carrier which operates to automatically position the plate so that a vertical beam of light sequentially passes through the individual wells. Absorbance of the light is measured in the manner typical for photometry, thereby giving a direct reading of the absorbance in each well, which can be related to the presence and amount of numerous light-absorbing substances.
Apparatuses for conducting vertical beam photometry are available commercially and have been utilized in numerous assays, such as enzyme-linked immunosorbent assays. However, there remains room for improvement in the microplates utilized in such assays, particularly improvements related to the reliability and reproducibility of measurements.